A touch sensor has been known as an interface for a user to input information to a display device. Arrangement of a touch sensor so as to overlap with a screen of a display device allows a user to operate input buttons, icons, and the like displayed on a screen, by which information can be readily input to a display device. For example, Japanese patent application publications No. 2015-50245 and No. 2011-23558 disclose an electronic apparatus in which a touch sensor is mounted over an organic EL (Electroluminescence) display device.